Pulsejets provide an inexpensive means to propel an aircraft or other propulsion device. Pulsejets as known in the art are extraordinarily simple devices, generally having only one moving part in the engine (a “mechanical” type air inlet valve). The main disadvantages of known pulsejet designs are a low propulsion efficiency and a limited mechanical durability due to the life expectancy of the air valve used in the engine. Pulsejet engine designs are therefore not commonly used as the main engines (i.e., the engine normally used for axial propulsion) of an aircraft.
In order to improve the thrust capability of a pulsejet engine, thrust augmentors, well known in the art, are often employed. By adding a thrust augmentor to the discharge side of a pulsejet engine, the thrust from the pulsejet engine can be increased by a factor ranging from approximately 1.5 to approximately 4.0. The drawback of known thrust augmentors is that the thrust augmentor itself is a separate structure added onto the pulsejet which increases the overall weight and air drag of the engine/augmentor combination. Because of the air inlet mechanical valve design, however, an augmented pulsejet engine is still not a good choice for the main propulsion engine of an aircraft due to its limited endurance, and propulsion inefficiency in applications where limited engine quantity is a design condition.
The air valve typically used on known pulsejet designs is a “mechanical” valve. The mechanical valve is typically located in the air inlet of a pulsejet engine and operates by deflecting to a minimum aperture size to allow air into the pulsejet engine. When a detonation of a fuel/air mixture occurs in the pulsejet engine, a backpressure wave from the detonation closes the mechanical valve, temporarily shutting off the air inlet to the pulsejet engine. Many mechanical valve designs known in the art suffer from a frequent mechanical failure rate and often fail from fatigue of the metal components used. The mechanical valve therefore becomes a limiting factor in the design life of a pulsejet engine, and therefore has reduced, the application of pulsejet engines.
The prior art also includes pulsejet engines with acoustic valves or valve-less designs. These designs, however, do not restrict engine combustion products from traversing back through the inlet. This backflow creates a loss in thrust unless (as in the case of a Hiller-Lockwood type pulsejet reactor) the inlet is pointed aft to provide thrust. The acoustic inlets suffer from severe performance losses. The reactors suffer from poor volumetric and integration considerations.
A need therefore exists for a pulsejet engine which reduces the maintenance and failure rate of existing designs due to the mechanical valve, and for an improved overall pulsejet/augmentor design to increase the potential uses of this otherwise simple engine type.